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Linux/mm/mremap.c

  1 /*
  2  *      mm/mremap.c
  3  *
  4  *      (C) Copyright 1996 Linus Torvalds
  5  *
  6  *      Address space accounting code   <alan@lxorguk.ukuu.org.uk>
  7  *      (C) Copyright 2002 Red Hat Inc, All Rights Reserved
  8  */
  9 
 10 #include <linux/mm.h>
 11 #include <linux/hugetlb.h>
 12 #include <linux/shm.h>
 13 #include <linux/ksm.h>
 14 #include <linux/mman.h>
 15 #include <linux/swap.h>
 16 #include <linux/capability.h>
 17 #include <linux/fs.h>
 18 #include <linux/swapops.h>
 19 #include <linux/highmem.h>
 20 #include <linux/security.h>
 21 #include <linux/syscalls.h>
 22 #include <linux/mmu_notifier.h>
 23 #include <linux/uaccess.h>
 24 #include <linux/mm-arch-hooks.h>
 25 
 26 #include <asm/cacheflush.h>
 27 #include <asm/tlbflush.h>
 28 
 29 #include "internal.h"
 30 
 31 static pmd_t *get_old_pmd(struct mm_struct *mm, unsigned long addr)
 32 {
 33         pgd_t *pgd;
 34         pud_t *pud;
 35         pmd_t *pmd;
 36 
 37         pgd = pgd_offset(mm, addr);
 38         if (pgd_none_or_clear_bad(pgd))
 39                 return NULL;
 40 
 41         pud = pud_offset(pgd, addr);
 42         if (pud_none_or_clear_bad(pud))
 43                 return NULL;
 44 
 45         pmd = pmd_offset(pud, addr);
 46         if (pmd_none(*pmd))
 47                 return NULL;
 48 
 49         return pmd;
 50 }
 51 
 52 static pmd_t *alloc_new_pmd(struct mm_struct *mm, struct vm_area_struct *vma,
 53                             unsigned long addr)
 54 {
 55         pgd_t *pgd;
 56         pud_t *pud;
 57         pmd_t *pmd;
 58 
 59         pgd = pgd_offset(mm, addr);
 60         pud = pud_alloc(mm, pgd, addr);
 61         if (!pud)
 62                 return NULL;
 63 
 64         pmd = pmd_alloc(mm, pud, addr);
 65         if (!pmd)
 66                 return NULL;
 67 
 68         VM_BUG_ON(pmd_trans_huge(*pmd));
 69 
 70         return pmd;
 71 }
 72 
 73 static void take_rmap_locks(struct vm_area_struct *vma)
 74 {
 75         if (vma->vm_file)
 76                 i_mmap_lock_write(vma->vm_file->f_mapping);
 77         if (vma->anon_vma)
 78                 anon_vma_lock_write(vma->anon_vma);
 79 }
 80 
 81 static void drop_rmap_locks(struct vm_area_struct *vma)
 82 {
 83         if (vma->anon_vma)
 84                 anon_vma_unlock_write(vma->anon_vma);
 85         if (vma->vm_file)
 86                 i_mmap_unlock_write(vma->vm_file->f_mapping);
 87 }
 88 
 89 static pte_t move_soft_dirty_pte(pte_t pte)
 90 {
 91         /*
 92          * Set soft dirty bit so we can notice
 93          * in userspace the ptes were moved.
 94          */
 95 #ifdef CONFIG_MEM_SOFT_DIRTY
 96         if (pte_present(pte))
 97                 pte = pte_mksoft_dirty(pte);
 98         else if (is_swap_pte(pte))
 99                 pte = pte_swp_mksoft_dirty(pte);
100 #endif
101         return pte;
102 }
103 
104 static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
105                 unsigned long old_addr, unsigned long old_end,
106                 struct vm_area_struct *new_vma, pmd_t *new_pmd,
107                 unsigned long new_addr, bool need_rmap_locks)
108 {
109         struct mm_struct *mm = vma->vm_mm;
110         pte_t *old_pte, *new_pte, pte;
111         spinlock_t *old_ptl, *new_ptl;
112 
113         /*
114          * When need_rmap_locks is true, we take the i_mmap_rwsem and anon_vma
115          * locks to ensure that rmap will always observe either the old or the
116          * new ptes. This is the easiest way to avoid races with
117          * truncate_pagecache(), page migration, etc...
118          *
119          * When need_rmap_locks is false, we use other ways to avoid
120          * such races:
121          *
122          * - During exec() shift_arg_pages(), we use a specially tagged vma
123          *   which rmap call sites look for using is_vma_temporary_stack().
124          *
125          * - During mremap(), new_vma is often known to be placed after vma
126          *   in rmap traversal order. This ensures rmap will always observe
127          *   either the old pte, or the new pte, or both (the page table locks
128          *   serialize access to individual ptes, but only rmap traversal
129          *   order guarantees that we won't miss both the old and new ptes).
130          */
131         if (need_rmap_locks)
132                 take_rmap_locks(vma);
133 
134         /*
135          * We don't have to worry about the ordering of src and dst
136          * pte locks because exclusive mmap_sem prevents deadlock.
137          */
138         old_pte = pte_offset_map_lock(mm, old_pmd, old_addr, &old_ptl);
139         new_pte = pte_offset_map(new_pmd, new_addr);
140         new_ptl = pte_lockptr(mm, new_pmd);
141         if (new_ptl != old_ptl)
142                 spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
143         arch_enter_lazy_mmu_mode();
144 
145         for (; old_addr < old_end; old_pte++, old_addr += PAGE_SIZE,
146                                    new_pte++, new_addr += PAGE_SIZE) {
147                 if (pte_none(*old_pte))
148                         continue;
149                 pte = ptep_get_and_clear(mm, old_addr, old_pte);
150                 pte = move_pte(pte, new_vma->vm_page_prot, old_addr, new_addr);
151                 pte = move_soft_dirty_pte(pte);
152                 set_pte_at(mm, new_addr, new_pte, pte);
153         }
154 
155         arch_leave_lazy_mmu_mode();
156         if (new_ptl != old_ptl)
157                 spin_unlock(new_ptl);
158         pte_unmap(new_pte - 1);
159         pte_unmap_unlock(old_pte - 1, old_ptl);
160         if (need_rmap_locks)
161                 drop_rmap_locks(vma);
162 }
163 
164 #define LATENCY_LIMIT   (64 * PAGE_SIZE)
165 
166 unsigned long move_page_tables(struct vm_area_struct *vma,
167                 unsigned long old_addr, struct vm_area_struct *new_vma,
168                 unsigned long new_addr, unsigned long len,
169                 bool need_rmap_locks)
170 {
171         unsigned long extent, next, old_end;
172         pmd_t *old_pmd, *new_pmd;
173         bool need_flush = false;
174         unsigned long mmun_start;       /* For mmu_notifiers */
175         unsigned long mmun_end;         /* For mmu_notifiers */
176 
177         old_end = old_addr + len;
178         flush_cache_range(vma, old_addr, old_end);
179 
180         mmun_start = old_addr;
181         mmun_end   = old_end;
182         mmu_notifier_invalidate_range_start(vma->vm_mm, mmun_start, mmun_end);
183 
184         for (; old_addr < old_end; old_addr += extent, new_addr += extent) {
185                 cond_resched();
186                 next = (old_addr + PMD_SIZE) & PMD_MASK;
187                 /* even if next overflowed, extent below will be ok */
188                 extent = next - old_addr;
189                 if (extent > old_end - old_addr)
190                         extent = old_end - old_addr;
191                 old_pmd = get_old_pmd(vma->vm_mm, old_addr);
192                 if (!old_pmd)
193                         continue;
194                 new_pmd = alloc_new_pmd(vma->vm_mm, vma, new_addr);
195                 if (!new_pmd)
196                         break;
197                 if (pmd_trans_huge(*old_pmd)) {
198                         if (extent == HPAGE_PMD_SIZE) {
199                                 bool moved;
200                                 /* See comment in move_ptes() */
201                                 if (need_rmap_locks)
202                                         take_rmap_locks(vma);
203                                 moved = move_huge_pmd(vma, old_addr, new_addr,
204                                                     old_end, old_pmd, new_pmd);
205                                 if (need_rmap_locks)
206                                         drop_rmap_locks(vma);
207                                 if (moved) {
208                                         need_flush = true;
209                                         continue;
210                                 }
211                         }
212                         split_huge_pmd(vma, old_pmd, old_addr);
213                         if (pmd_trans_unstable(old_pmd))
214                                 continue;
215                 }
216                 if (pte_alloc(new_vma->vm_mm, new_pmd, new_addr))
217                         break;
218                 next = (new_addr + PMD_SIZE) & PMD_MASK;
219                 if (extent > next - new_addr)
220                         extent = next - new_addr;
221                 if (extent > LATENCY_LIMIT)
222                         extent = LATENCY_LIMIT;
223                 move_ptes(vma, old_pmd, old_addr, old_addr + extent,
224                           new_vma, new_pmd, new_addr, need_rmap_locks);
225                 need_flush = true;
226         }
227         if (likely(need_flush))
228                 flush_tlb_range(vma, old_end-len, old_addr);
229 
230         mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end);
231 
232         return len + old_addr - old_end;        /* how much done */
233 }
234 
235 static unsigned long move_vma(struct vm_area_struct *vma,
236                 unsigned long old_addr, unsigned long old_len,
237                 unsigned long new_len, unsigned long new_addr, bool *locked)
238 {
239         struct mm_struct *mm = vma->vm_mm;
240         struct vm_area_struct *new_vma;
241         unsigned long vm_flags = vma->vm_flags;
242         unsigned long new_pgoff;
243         unsigned long moved_len;
244         unsigned long excess = 0;
245         unsigned long hiwater_vm;
246         int split = 0;
247         int err;
248         bool need_rmap_locks;
249 
250         /*
251          * We'd prefer to avoid failure later on in do_munmap:
252          * which may split one vma into three before unmapping.
253          */
254         if (mm->map_count >= sysctl_max_map_count - 3)
255                 return -ENOMEM;
256 
257         /*
258          * Advise KSM to break any KSM pages in the area to be moved:
259          * it would be confusing if they were to turn up at the new
260          * location, where they happen to coincide with different KSM
261          * pages recently unmapped.  But leave vma->vm_flags as it was,
262          * so KSM can come around to merge on vma and new_vma afterwards.
263          */
264         err = ksm_madvise(vma, old_addr, old_addr + old_len,
265                                                 MADV_UNMERGEABLE, &vm_flags);
266         if (err)
267                 return err;
268 
269         new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT);
270         new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff,
271                            &need_rmap_locks);
272         if (!new_vma)
273                 return -ENOMEM;
274 
275         moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len,
276                                      need_rmap_locks);
277         if (moved_len < old_len) {
278                 err = -ENOMEM;
279         } else if (vma->vm_ops && vma->vm_ops->mremap) {
280                 err = vma->vm_ops->mremap(new_vma);
281         }
282 
283         if (unlikely(err)) {
284                 /*
285                  * On error, move entries back from new area to old,
286                  * which will succeed since page tables still there,
287                  * and then proceed to unmap new area instead of old.
288                  */
289                 move_page_tables(new_vma, new_addr, vma, old_addr, moved_len,
290                                  true);
291                 vma = new_vma;
292                 old_len = new_len;
293                 old_addr = new_addr;
294                 new_addr = err;
295         } else {
296                 arch_remap(mm, old_addr, old_addr + old_len,
297                            new_addr, new_addr + new_len);
298         }
299 
300         /* Conceal VM_ACCOUNT so old reservation is not undone */
301         if (vm_flags & VM_ACCOUNT) {
302                 vma->vm_flags &= ~VM_ACCOUNT;
303                 excess = vma->vm_end - vma->vm_start - old_len;
304                 if (old_addr > vma->vm_start &&
305                     old_addr + old_len < vma->vm_end)
306                         split = 1;
307         }
308 
309         /*
310          * If we failed to move page tables we still do total_vm increment
311          * since do_munmap() will decrement it by old_len == new_len.
312          *
313          * Since total_vm is about to be raised artificially high for a
314          * moment, we need to restore high watermark afterwards: if stats
315          * are taken meanwhile, total_vm and hiwater_vm appear too high.
316          * If this were a serious issue, we'd add a flag to do_munmap().
317          */
318         hiwater_vm = mm->hiwater_vm;
319         vm_stat_account(mm, vma->vm_flags, new_len >> PAGE_SHIFT);
320 
321         /* Tell pfnmap has moved from this vma */
322         if (unlikely(vma->vm_flags & VM_PFNMAP))
323                 untrack_pfn_moved(vma);
324 
325         if (do_munmap(mm, old_addr, old_len) < 0) {
326                 /* OOM: unable to split vma, just get accounts right */
327                 vm_unacct_memory(excess >> PAGE_SHIFT);
328                 excess = 0;
329         }
330         mm->hiwater_vm = hiwater_vm;
331 
332         /* Restore VM_ACCOUNT if one or two pieces of vma left */
333         if (excess) {
334                 vma->vm_flags |= VM_ACCOUNT;
335                 if (split)
336                         vma->vm_next->vm_flags |= VM_ACCOUNT;
337         }
338 
339         if (vm_flags & VM_LOCKED) {
340                 mm->locked_vm += new_len >> PAGE_SHIFT;
341                 *locked = true;
342         }
343 
344         return new_addr;
345 }
346 
347 static struct vm_area_struct *vma_to_resize(unsigned long addr,
348         unsigned long old_len, unsigned long new_len, unsigned long *p)
349 {
350         struct mm_struct *mm = current->mm;
351         struct vm_area_struct *vma = find_vma(mm, addr);
352         unsigned long pgoff;
353 
354         if (!vma || vma->vm_start > addr)
355                 return ERR_PTR(-EFAULT);
356 
357         if (is_vm_hugetlb_page(vma))
358                 return ERR_PTR(-EINVAL);
359 
360         /* We can't remap across vm area boundaries */
361         if (old_len > vma->vm_end - addr)
362                 return ERR_PTR(-EFAULT);
363 
364         if (new_len == old_len)
365                 return vma;
366 
367         /* Need to be careful about a growing mapping */
368         pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
369         pgoff += vma->vm_pgoff;
370         if (pgoff + (new_len >> PAGE_SHIFT) < pgoff)
371                 return ERR_PTR(-EINVAL);
372 
373         if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))
374                 return ERR_PTR(-EFAULT);
375 
376         if (vma->vm_flags & VM_LOCKED) {
377                 unsigned long locked, lock_limit;
378                 locked = mm->locked_vm << PAGE_SHIFT;
379                 lock_limit = rlimit(RLIMIT_MEMLOCK);
380                 locked += new_len - old_len;
381                 if (locked > lock_limit && !capable(CAP_IPC_LOCK))
382                         return ERR_PTR(-EAGAIN);
383         }
384 
385         if (!may_expand_vm(mm, vma->vm_flags,
386                                 (new_len - old_len) >> PAGE_SHIFT))
387                 return ERR_PTR(-ENOMEM);
388 
389         if (vma->vm_flags & VM_ACCOUNT) {
390                 unsigned long charged = (new_len - old_len) >> PAGE_SHIFT;
391                 if (security_vm_enough_memory_mm(mm, charged))
392                         return ERR_PTR(-ENOMEM);
393                 *p = charged;
394         }
395 
396         return vma;
397 }
398 
399 static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
400                 unsigned long new_addr, unsigned long new_len, bool *locked)
401 {
402         struct mm_struct *mm = current->mm;
403         struct vm_area_struct *vma;
404         unsigned long ret = -EINVAL;
405         unsigned long charged = 0;
406         unsigned long map_flags;
407 
408         if (offset_in_page(new_addr))
409                 goto out;
410 
411         if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
412                 goto out;
413 
414         /* Ensure the old/new locations do not overlap */
415         if (addr + old_len > new_addr && new_addr + new_len > addr)
416                 goto out;
417 
418         ret = do_munmap(mm, new_addr, new_len);
419         if (ret)
420                 goto out;
421 
422         if (old_len >= new_len) {
423                 ret = do_munmap(mm, addr+new_len, old_len - new_len);
424                 if (ret && old_len != new_len)
425                         goto out;
426                 old_len = new_len;
427         }
428 
429         vma = vma_to_resize(addr, old_len, new_len, &charged);
430         if (IS_ERR(vma)) {
431                 ret = PTR_ERR(vma);
432                 goto out;
433         }
434 
435         map_flags = MAP_FIXED;
436         if (vma->vm_flags & VM_MAYSHARE)
437                 map_flags |= MAP_SHARED;
438 
439         ret = get_unmapped_area(vma->vm_file, new_addr, new_len, vma->vm_pgoff +
440                                 ((addr - vma->vm_start) >> PAGE_SHIFT),
441                                 map_flags);
442         if (offset_in_page(ret))
443                 goto out1;
444 
445         ret = move_vma(vma, addr, old_len, new_len, new_addr, locked);
446         if (!(offset_in_page(ret)))
447                 goto out;
448 out1:
449         vm_unacct_memory(charged);
450 
451 out:
452         return ret;
453 }
454 
455 static int vma_expandable(struct vm_area_struct *vma, unsigned long delta)
456 {
457         unsigned long end = vma->vm_end + delta;
458         if (end < vma->vm_end) /* overflow */
459                 return 0;
460         if (vma->vm_next && vma->vm_next->vm_start < end) /* intersection */
461                 return 0;
462         if (get_unmapped_area(NULL, vma->vm_start, end - vma->vm_start,
463                               0, MAP_FIXED) & ~PAGE_MASK)
464                 return 0;
465         return 1;
466 }
467 
468 /*
469  * Expand (or shrink) an existing mapping, potentially moving it at the
470  * same time (controlled by the MREMAP_MAYMOVE flag and available VM space)
471  *
472  * MREMAP_FIXED option added 5-Dec-1999 by Benjamin LaHaise
473  * This option implies MREMAP_MAYMOVE.
474  */
475 SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
476                 unsigned long, new_len, unsigned long, flags,
477                 unsigned long, new_addr)
478 {
479         struct mm_struct *mm = current->mm;
480         struct vm_area_struct *vma;
481         unsigned long ret = -EINVAL;
482         unsigned long charged = 0;
483         bool locked = false;
484 
485         if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE))
486                 return ret;
487 
488         if (flags & MREMAP_FIXED && !(flags & MREMAP_MAYMOVE))
489                 return ret;
490 
491         if (offset_in_page(addr))
492                 return ret;
493 
494         old_len = PAGE_ALIGN(old_len);
495         new_len = PAGE_ALIGN(new_len);
496 
497         /*
498          * We allow a zero old-len as a special case
499          * for DOS-emu "duplicate shm area" thing. But
500          * a zero new-len is nonsensical.
501          */
502         if (!new_len)
503                 return ret;
504 
505         if (down_write_killable(&current->mm->mmap_sem))
506                 return -EINTR;
507 
508         if (flags & MREMAP_FIXED) {
509                 ret = mremap_to(addr, old_len, new_addr, new_len,
510                                 &locked);
511                 goto out;
512         }
513 
514         /*
515          * Always allow a shrinking remap: that just unmaps
516          * the unnecessary pages..
517          * do_munmap does all the needed commit accounting
518          */
519         if (old_len >= new_len) {
520                 ret = do_munmap(mm, addr+new_len, old_len - new_len);
521                 if (ret && old_len != new_len)
522                         goto out;
523                 ret = addr;
524                 goto out;
525         }
526 
527         /*
528          * Ok, we need to grow..
529          */
530         vma = vma_to_resize(addr, old_len, new_len, &charged);
531         if (IS_ERR(vma)) {
532                 ret = PTR_ERR(vma);
533                 goto out;
534         }
535 
536         /* old_len exactly to the end of the area..
537          */
538         if (old_len == vma->vm_end - addr) {
539                 /* can we just expand the current mapping? */
540                 if (vma_expandable(vma, new_len - old_len)) {
541                         int pages = (new_len - old_len) >> PAGE_SHIFT;
542 
543                         if (vma_adjust(vma, vma->vm_start, addr + new_len,
544                                        vma->vm_pgoff, NULL)) {
545                                 ret = -ENOMEM;
546                                 goto out;
547                         }
548 
549                         vm_stat_account(mm, vma->vm_flags, pages);
550                         if (vma->vm_flags & VM_LOCKED) {
551                                 mm->locked_vm += pages;
552                                 locked = true;
553                                 new_addr = addr;
554                         }
555                         ret = addr;
556                         goto out;
557                 }
558         }
559 
560         /*
561          * We weren't able to just expand or shrink the area,
562          * we need to create a new one and move it..
563          */
564         ret = -ENOMEM;
565         if (flags & MREMAP_MAYMOVE) {
566                 unsigned long map_flags = 0;
567                 if (vma->vm_flags & VM_MAYSHARE)
568                         map_flags |= MAP_SHARED;
569 
570                 new_addr = get_unmapped_area(vma->vm_file, 0, new_len,
571                                         vma->vm_pgoff +
572                                         ((addr - vma->vm_start) >> PAGE_SHIFT),
573                                         map_flags);
574                 if (offset_in_page(new_addr)) {
575                         ret = new_addr;
576                         goto out;
577                 }
578 
579                 ret = move_vma(vma, addr, old_len, new_len, new_addr, &locked);
580         }
581 out:
582         if (offset_in_page(ret)) {
583                 vm_unacct_memory(charged);
584                 locked = 0;
585         }
586         up_write(&current->mm->mmap_sem);
587         if (locked && new_len > old_len)
588                 mm_populate(new_addr + old_len, new_len - old_len);
589         return ret;
590 }
591 

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